ASTM_A_561_-_08_2014.pdf

Designation:A56108(Reapproved 2014)Standard Practice forMacroetch Testing of Tool Steel Bars1This standard is issued under the fixed designation A561;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S.Department of Defense.1.Scope1.1 This practice for macroetch testing has been found to bea useful and reliable method for evaluating the quality of toolsteel bars.It is used as a quality control and inspection test toreveal by deep acid etching the macrostructure in specimenscut from bars and to show the presence of such conditions aspipe,cracks,porosity,segregation,or foreign material.Theetched surface is generally examined visually,but magnifica-tion up to about 10 is occasionally employed.1.2 The values stated in inch-pound units are to be regardedas standard.The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.2.Referenced Documents2.1 ASTM Adjuncts:2Six Photomacrographs3.Apparatus3.1 Etching ContainersMacroetching may be performedin a vessel of borosilicate glass,porcelain,corrosion-resistantmetals,or some other acid-resisting material.4.Reagent4.1 Etching ReagentA solution of equal volumes of con-centrated hydrochloric acid(HCl,sp gr 1.19)and water iscommonly used for macroetching tool steels.This solutionmust be used under a ventilating hood because HCl is volatileand the fumes are corrosive and irritating,although nontoxic.The solution may be reused within limits.With use,theconcentration of dissolved iron and other metals increases andthe acidity of the solution decreases retarding the etchingaction.Spent solution shall be replaced with fresh solution,notreplenished with concentrated acid.5.Sampling5.1 The selection of specimens for macroetch testing mustbe done with care for interpretations to be of value.5.1.1 Specimens are usually cut from hot-rolled annealedbars,but may be cut from machined or ground bars if the barsare to be finish machined or ground.5.1.2 The specimen should be located at a sufficient distancefrom the end of the bar to avoid end effects.5.1.3 For ease in handling,use specimens14to12in.(6.35to 12.7 mm)thick.5.1.4 Cut specimens to expose a transverse section of thebar;however,the test is occasionally performed on a longitu-dinal section.5.1.5 Specimens may be taken from one or both ends of abar.Each bar may be sampled,or a few typical specimens maybe tested as representative of a large number of bars.6.Specimen Preparation6.1 In all cutting and grinding operations on the specimen,care must be exercised to avoid heating the surface to anexcessively high temperature.Specimens are cut from bars bysawing,machining,abrasive wheel cutting,or other means.Cutting should be controlled to prevent smearing the cut faceand masking the structure.6.1.1 The“as-cut”surface of a specimen may be sufficientlysmooth to reveal the defects for which the examination isconducted.No additional surface preparation may then benecessary.6.1.2 Additional surface preparation may be required toremove cutting marks and to allow details to be revealed byetching.In such circumstances,machining,grinding,or pol-ishing may be necessary.Generally,the degree of surfacesmoothness required is greater the finer the detail that must beresolved.When the action of the etchant is drastic,a coarsersurface finish may be used.6.1.3 The surface must be free of adhering grease and oil.There should be no scale or oxide on the surface which will beexamined after etching.7.Procedure7.1 Temperature for MacroetchingEtching characteristicsare influenced markedly by the temperature of the etchant.1This practice is under the jurisdiction of ASTM Committee A01 on Steel,Stainless Steel and Related Alloysand is the direct responsibility of SubcommitteeA01.29 on Tool Steels.Current edition approved March 1,2014.Published March 2014.Originallyapproved in 1966.Last previous edition approved in 2008 as A561 08.DOI:10.1520/A0561-08R14.2Available from ASTM International Headquarters.Order Adjunct No.ADJA0561.Original adjunct produced in 1984.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 Thus,the reagent temperature should be controlled for mac-roetching if comparative results are desired.Tool steels aregenerally macroetched at about 160F(71C).At thistemperature,the etching reaction is vigorous and solutionlosses through evaporation are not excessive.The solution maybe heated on a gas or electric hot plate,by an acid-proofimmersion heater,or by steam.7.2 Etching TimeThe etching time should be sufficientlylong to completely reveal the structure in the specimen,yetshould not be so long as to develop a